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IMPRINT LITHOGRAPHY
Presented By
Sujeet Kumar
Contains
-Different type of Lithography
-Why Imprint Lithography
-Process of Lithography
-Scheme
-Application
-Current situation
-Future
Different type of lithography
1.UV Lithography
2.X-ray Lithography
3.Electron-beam Lithography
4. Imprint Lithography
1.UV Lithography
• It uses 2000 to 4000 Å wavelength
• Hence, diffraction effects
• Feature size 1-3 micro meter
2. X-ray lithography
• This lithography uses wavelength of 4 to
50 Å is much shorter than that of UV light
(2000 to 4000 Å). Hence, diffraction
effects are reduced and higher resolution
can be attained
• 250 nm feature size in research and 500
nm has obtained
Problems
-On account of the finite size of the x-ray source and the finite mask-to-wafer
gap, a penumbral effect results which degrades the resolution at the edge of a
feature.
-An additional geometric effect is the lateral magnification error due to the finite
mask-to-wafer gap and the non-vertical incidence of the x-ray beam. The
projected images of the mask are shifted laterally by an amount d, called
runout. This runout error must be compensated for during the mask making
process.
3.Electron-beam lithography
3.Electron-beam lithography
• The advantages of electron lithography
are:
(1) Generation of micron and submicron
resist geometries
(2) Highly automated and precisely
controlled operation
(3) Greater depth of focus
(4) Direct patterning without a mask
3.Electron-beam lithography
• The biggest disadvantage of electron
lithography is its low throughput
(approximately 5 wafers/hour at less than
0.1 µ resolution). Therefore, electron
lithography is primarily used in the
production of photo masks and in
situations that require small number of
custom circuits.
• Electron scattering in resist and
substrate
• The scattered electrons also
expose the resist
• Interaction of e-and substrate + resist
leads to beam spreading
– Elastic and in-elastic scattering in the resist
– Back-scattering from substrate and
generation of secondary e– 100 Å e-beam become 0.2 µm line
Why Imprint Lithography
• Nanoimprint lithography is a simple pattern
transfer process that is neither limited by
diffraction nor scattering effects nor
secondary electrons, and does not require
any sophisticated radiation chemistry
• Its advantages are low cost, high
throughput, relatively high pattern
resolution and compatibility with the
existing technologies
History
• Nanoimprint lithography was first invented
by Prof. Stephen Chou and his students.
Soon after its invention, a lot of
researchers developed many different
variations and implementations.
• At this point, nanoimprint lithography has
been added to the International
Technology Roadmap for Semiconductors
(ITRS) for the 32 and 22 nm nodes.
Process
1.Thermoplastic nanoimprint
lithography
2. Photo nanoimprint lithography
3. Electrochemical nanoimprinting
1.Thermoplastic nanoimprint
lithography
Mold(Si or
Nickel)
Template generation
Different Series of Thermoplastic
Polymer
Reactive Ion Etching(RIE)
• Etching gas is introduced
into the chamber continuously
• Plasma is created by RF
power
•Reactive species (radicals
and ions) are generated in the plasma
radicals: chemical reaction
ions: bombardment
Reactive Ion Etching(RIE)
•Reactive species diffused
onto the sample surface
•The species are absorbed
by the surface
•Chemical reaction occurs,
forming volatile byproduct
•Byproduct is desorbed from the surface
•Byproduct is exhausted from the chamber
RIE gases
2.Photo nano imprint
lithography
-Invented by Willson et al
Template generation
• Method uses a much thinner (15 nm) layer
of Cr as a hardmask. This sub-20 nm Cr
layer acts as a sufficient hardmask during
the etching of the glass substrate because
of the high etch selectivity of glass to Cr in
a fluorine-based process.
Release layer
-Teflon AF (Amorphous fluoropolymers)
has good thermal stability and chemical
resistance along with a very low surface
energy .
-Cytop
Etch barrier
The UV-curable etch barrier a solution of
organic monomer, silylated monomer, and
dimethyl siloxane oligomer (DMS)
• -The silylated monomers and the DMS
provide the silicon required to give a highoxygen etch resistance also lower the
surface energy of the etch barrier.
Transfer layer
• The transfer layers are formed from materials
thermoset polymers, thermoplastic polymers,
polyepoxies, polyamides, polyurethanes,
polycarbonates, polyesters, and combinations.
• The transfer layer is fabricated in such a manner
so as to possess a continuous, smooth,
relatively defect-free surface that may exhibit
excellent adhesion to the polymerizable fluid.
3.Electrochemical nanoimprinting
• Electrochemical nanoimprinting can be achieved using a template
made from a super ionic conductor such as silver sulfide .
• When the template is contacted with metal, electrochemical etching
can be carried out with an applied voltage.
• proceeds as it selectively removes material from a the metal
substrate with a controlled electrical potential, and concludes with
the formation a complementary pattern at the contact
Characteristics
• Features down to 50 nm on silver films of
thicknesses ranging from 50 to 500 nm.
• As the process is conducted in an
ambient environment and does not involve
the use of liquids, it displays potential for
single-step, high-throughput, large-area
manufacturing of metallic nanostructures.
Scheme
There are two scheme which is used in all
Imprint lithography
1.Full Wafer Nanoimprint
2. Step and repeat nanoimprint
1.Full Wafer Nanoimprint
- In a full wafer nanoimprint scheme, all the
patterns are contained in a single
nanoimprint field and will be transferred in
a single imprint step. This allows a high
throughput and uniformity.
- At least 8-inch (20 cm) diameter full-wafer
nanoimprint with high fidelity is possible
2. Step and repeat nanoimprint
-The imprint field (die) is typically much smaller than the
full wafer nanoimprint field. The die is repeatedly
imprinted to the substrate with certain step size.
-This scheme is good for nanoimprint mold creation .It is
currently limited by the throughput, alignment and street
width issues
Application
• Nanoimprint lithography has been used to fabricate
devices for electrical, optical, photonic and biological
applications.
• For electronics devices, NIL has been used to fabricate
MOSFET, O-TFT, single electron memory (Si singleelectron memories using nanoimprint lithography (NIL).
The devices consist of a narrow channel metal-oxidesemiconductor field-effect transistor and a sub-10-nm
storage dot, which is located between the channel and
the gate ).
Application
-MSM (metal-semiconductor-metal)
Photo detector: suited for measurements of
optical high speed waveform and optical
communications
Current Situation
- For optics and photonics, intensive study has been conducted in
fabrication of sub wavelength resonant grating filter, polarizer, wave
plate, anti-reflective structures, integrated photonics circuit and
plasmontic devices by NIL(Picture in next slide)
- sub-10 nm nanofluidic channels had been fabricated using NIL and
used in DNA strenching experiment.
- Currently, NIL is used to shrink the size of biomolecular sorting
device an order of magnitude smaller and more efficient.
- Researchers, working for lower cost templates using conventional
micro-fabrication tools such as chemical vapor deposition (CVD)
systems to deposit alternate layers of thin films and then etching the
alternate layers with high selectivity over the other layers
sub wavelength resonant
grating filter
Future
- It is possible that self-assembled structures will provide
the ultimate solution for templates of periodic patterns at
scales of 10 nm and less. It is also possible to resolve
the template generation issue by using a programmable
template.